Meath U.S. Pat. No. 2,462,413 discloses a scheme for the production of formaldehyde involving the oxidation of air-methanol mixtures in a two-stage conversion process with interstage cooling. While such a process is successful in controlling the temperature of reaction during oxidation and thereby minimizing decomposition of formaldehyde and product formed, it offers as a disadvantage a relatively high leakage of unconverted methanol. This makes it difficult to operate such a process to manufacture high strength aqueous formaldehyde solutions, such as 60% formaldehyde, containing less than 2% methanol.
It has been found in accordance with the present invention that such a two-stage conversion process yielding a high strength formaldehyde product containing low concentrations of methanol can be obtained by use of significantly higher space velocities in the second stage converter, together with the use of a silver catalyst in a specified form and size.